Arthropod Motion-Sensing Hairs: Biological Models for Micro-Electro-Mechanical Systems

The filiform hairs of terrestrial and aquatic arthropods are uniquely sensitive medium motion sensors, refined by natural selection pressures over hundreds of millions of years. These sensors provide biological models for the design and fabrication of corresponding artificial sensors that could be used for fundamental research as well as practical applications. However, the measurement and modeling of filiform hairs poses a highly complex interdisciplinary problem involving various facets of biology, mechanics and mathematics. Specifically, it is of special interest to uncover the basic “design” principles affecting the maximum angular deflection and maximum angular velocity, and their respective resonance frequencies, of the hairs as a function of the physical parameters that affect these four quantities. To this end, the physically-approximate theoretical analysis of Humphrey et al. (2000) is used to predict and understand the performance characteristics of single hairs. Calculated results obtained using the approximate analysis compare well with corresponding results from a more exact physical analysis and with previous measurements and calculations, showing that all qualitative aspects of hair behavior are correctly captured by the simplified theory. The theory is then used to explain the dependence of hair motion on the physical parameters that affect it. The findings of this study suggest that an artificial motion-sensing micro-electro-mechanical system (MEMS), patterned along the lines of an array of hairs, could be designed to detect and resolve the temporal and spatial characteristics of unsteady flow structures in the near-wall region of boundary layer flows.